apply_filters()应用过滤器

功能:

apply_filters()函数用来创建一个过滤器,大多数被用在函数中,是 WordPress 插件机制中非常重要的一个函数,能让其它的主题和插件对一个值进行修改过滤。

用法:

<?php apply_filters( $tag, $value, $var... );?>

参数:

$tag

(字符串)(必须)过滤器的名字。

默认值:None

$value

(混合)(必须)要过滤的值,如果没人过滤则直接返回这个值。

$var

(混合) (可选)传给过滤函数额外的变量参数,辅助过滤函数对返回值进行操作,可以添加无限个。

返回值:

(混合)过滤后的值,如果没人过滤则直接返回 $value 的值。

所在位置:

apply_filters()函数包含在wp-includes/plugin.php中.

源码:

/**
 * Call the functions added to a filter hook.
 *
 * The callback functions attached to filter hook $tag are invoked by calling
 * this function. This function can be used to create a new filter hook by
 * simply calling this function with the name of the new hook specified using
 * the $tag parameter.
 *
 * The function allows for additional arguments to be added and passed to hooks.
 *
 *     // Our filter callback function
 *     function example_callback( $string, $arg1, $arg2 ) {
 *         // (maybe) modify $string
 *         return $string;
 *     }
 *     add_filter( 'example_filter', 'example_callback', 10, 3 );
 *
 *     /*
 *      * Apply the filters by calling the 'example_callback' function we
 *      * "hooked" to 'example_filter' using the add_filter() function above.
 *      * - 'example_filter' is the filter hook $tag
 *      * - 'filter me' is the value being filtered
 *      * - $arg1 and $arg2 are the additional arguments passed to the callback.
 *     $value = apply_filters( 'example_filter', 'filter me', $arg1, $arg2 );
 *
 * @since 0.71
 *
 * @global array $wp_filter         Stores all of the filters.
 * @global array $merged_filters    Merges the filter hooks using this function.
 * @global array $wp_current_filter Stores the list of current filters with the current one last.
 *
 * @param string $tag   The name of the filter hook.
 * @param mixed  $value The value on which the filters hooked to `$tag` are applied on.
 * @param mixed  $var   Additional variables passed to the functions hooked to `$tag`.
 * @return mixed The filtered value after all hooked functions are applied to it.
 */
function apply_filters( $tag, $value ) {
	global $wp_filter, $merged_filters, $wp_current_filter;
 
	$args = array();
 
	// Do 'all' actions first.
	if ( isset($wp_filter['all']) ) {
		$wp_current_filter[] = $tag;
		$args = func_get_args();
		_wp_call_all_hook($args);
	}
 
	if ( !isset($wp_filter[$tag]) ) {
		if ( isset($wp_filter['all']) )
			array_pop($wp_current_filter);
		return $value;
	}
 
	if ( !isset($wp_filter['all']) )
		$wp_current_filter[] = $tag;
 
	// Sort.
	if ( !isset( $merged_filters[ $tag ] ) ) {
		ksort($wp_filter[$tag]);
		$merged_filters[ $tag ] = true;
	}
 
	reset( $wp_filter[ $tag ] );
 
	if ( empty($args) )
		$args = func_get_args();
 
	do {
		foreach( (array) current($wp_filter[$tag]) as $the_ )
			if ( !is_null($the_['function']) ){
				$args[1] = $value;
				$value = call_user_func_array($the_['function'], array_slice($args, 1, (int) $the_['accepted_args']));
			}
 
	} while ( next($wp_filter[$tag]) !== false );
 
	array_pop( $wp_current_filter );
 
	return $value;
}

示例:

echo apply_filters( 'test', '可以被修改的值' );

相关函数:

add_filter();
remove_filter();

(完)

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